Cisco MWR 2941-DC Router Overview

The Cisco MWR 2941-DC Mobile Wireless Router is a cell-site access platform specifically designed to optimize, aggregate, and transport mixed-generation radio access network (RAN) traffic. The router is used at the cell site edge as a part of a 2G, 3G, or 4G radio access network (RAN).

The Cisco MWR 2941-DC helps enable a variety of RAN solutions by extending IP connectivity to devices using Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), Node Bs using HSPA or LTE, base transceiver stations (BTSs) using Enhanced Data Rates for GSM Evolution (EDGE), Division Multiple Access (CDMA), CDMA-2000, EVDO, or WiMAX, and other cell-site equipment. It transparently and efficiently transports cell-site voice, data, and signaling traffic over IP using traditional T1/E1 circuits, including leased line, microwave, and satellite, as well as alternative backhaul networks, including Carrier Ethernet, DSL, Ethernet in the First Mile (EFM), and WiMAX. It also supports standards-based Internet Engineering Task Force (IETF) Internet protocols over the RAN transport network, including those standardized at the Third-Generation Partnership Project (3GPP) for IP RAN transport.

Custom designed for the cell site, the Cisco MWR 2941-DC features a small form factor, extended operating temperature, and cell-site DC input voltages.

Introduction

A typical RAN is composed of thousands of base transceiver stations (BTSs)/Node Bs, hundreds of base station controllers/radio network controllers (BSCs/RNCs), and several mobile switching centers (MSCs). The BTS/Node Bs and BSC/RNC are often separated by large geographic distances, with the BTSs/Node Bs located in cell sites uniformly distributed throughout a region, and the BSCs, RNCs, and MSCs located at suitably chosen Central Offices (CO) or mobile telephone switching offices (MTSO).

The traffic generated by a BTS/Node B is transported to the corresponding BSC/RNC across a network, referred to as the backhaul network, which is often a hub-and-spoke topology with hundreds of BTS/Node Bs connected to a BSC/RNC by point-to-point time division multiplexing (TDM) trunks. These TDM trunks may be leased-line T1/E1s or their logical equivalents, such as microwave links or satellite channels.

Features

The following sections describe the features available in the Cisco MWR 2941-DC router.

Cisco Pseudowire Emulation Edge-to-Edge

Cisco Pseudowire Emulation Edge-to-Edge (PWE3) is a mechanism that emulates the essential attributes of a service, such as EI/T1 (Figure 1-1).

Figure 1-1 Cisco MWR 2941-DC Router in a PWE3—Example

The required functions of pseudowires (PWs) include encapsulating service-specific packet data units (PDUs) arriving at an ingress port and carrying them across a path or tunnel, managing their timing and order, and other operations required to emulate the behavior of the service efficiently.

PW is perceived as an unshared link or circuit of the chosen service. However, there may be deficiencies that impede some applications from being carried on a PW. These limitations should be fully described in the appropriate service-specific documents and applicability statements.

A PW is a connection between two provider edge (PE) devices, which connects two attachment circuits (ACs). An AC can be a VPI/VCI or an T1/E1 link.

Structure-agnostic TDM over Packet

SAToP encapsulates TDM bit-streams (T1, E1, T3, E3) as PWs over PSNs. It disregards any structure that may be imposed on streams, in particular the structure imposed by the standard TDM framing.

The protocol used for emulation of these services does not depend on the method in which attachment circuits are delivered to the PEs. For example, a T1 attachment circuit is treated the same way for all delivery methods, including: PE on copper, multiplex in a T3 circuit, mapped into a virtual tributary of a SONET/SDH circuit, or carried over a network using unstructured Circuit Emulation Service (CES). Termination of specific carrier layers used between the PE and circuit emulation (CE) is performed by an appropriate network service provider (NSP).

CESoPSN encapsulates structured (NxDS0) TDM signals as PWs over PSNs. It complements similar work for structure-agnostic emulation of TDM bit-streams, such as PWE3-SAToP.

Emulation of NxDS0 circuits saves PSN bandwidth and supports DS0-level grooming and distributed cross-connect applications. It also enhances resilience of CE devices due to the effects of loss of packets in the PSN.

Transportation of Service Using ATM over MPLS

An Asynchronous Transfer Mode (ATM) PW is used to carry ATM cells over an MPLS network. It is an evolutionary technology that allows you to migrate packet networks from legacy networks, yet provides transport for legacy applications. ATM over MPLS is particularly useful for transporting 3G voice traffic over MPLS networks.

You can configure ATM over MPLS in the following modes:

N-to-1 Cell Mode—Maps one or more ATM virtual channel connections (VCCs) or virtual permanent connection (VPCs) to a single pseudowire.

1-to-1 Cell Mode—Maps a single ATM VCC or VPC to a single pseudowire.

Port Mode—Map one physical port to a single pseudowire connection.

The Cisco MWR 2941-DC also supports cell packing and PVC mapping for ATM over MPLS pseudowires.

GSM Abis Optimization over IP Implementation

GSM Abis refers to the interface between the BTS and BSC in GSM system (the same term is used for CDMA systems). The Cisco MWR 2941-DC implementation of GSM Abis optimization over IP allows carriers to optimize voice and data traffic and maximize effective utilization of E1/T1 backhaul connections. Figure 1-2 shows a Cisco MWR 2941-DC router in a network using GSM Abis Optimization over IP.

The Cisco GSM Abis optimization solution increases the T1/E1 bandwidth efficiency by as much as 50 percent:

1. Traffic loads can be carried using half as many T1/E1 trunks as previously used, allowing more voice and data calls to be carried over the existing RAN backhaul network.

2. The need to add new T1/E1 trunks is eliminated as traffic demands grow.

3. Existing trunks can be decommissioned (ending recurring costs).

Excess capacity is available in the existing RAN backhaul network. The operator can reallocate recovered bandwidth to carry traffic from other radios, such as GPRS, EDGE, 1xEV-DO, PWLANs, and other data overlays. The operator avoids costs of supplementing backhaul capacity. It also accelerates time to revenue from deployments of new radio technologies, as there is no need for the operator to be delayed until additional microwave licenses or leased-lines are supplied.

Bidirectional Forwarding Detection

Bidirectional Forwarding Detection (BFD) provides a low-overhead, short-duration method of detecting failures in the forwarding path between two adjacent routers, including the interfaces, data links, and forwarding planes. BFD is a detection protocol that you enable at the interface and routing protocol levels. For instructions on how to configure BFD, see the “Configuring BFD” section.

Intelligent Cell Site IP Services

The Cisco RAN-O and IP-RAN solutions allow you to deliver profit-enhancing services. This is achieved through the set of IP networking features supported in Cisco IOS software that extends to the cell site (see Figure 1-3).

Cell Site Points-of-Presence

The cell site becomes a physical Point-of-Presence (POP) from which to offer hotspot services, or voice and wired ISP services, to nearby enterprises and residences. Because many cell sites are located in and around downtown areas, hotels, airports, and convention centers, they make attractive sites for co-locating public wireless LAN (PWLAN) access points and other wireless data overlays. Many of these wireless data radios are IP-based. IP networking features, like Mobile IP, VoIP, IP Multicast, VPN, and content caching, enable delivery of new revenue-generating services over these radios. The corresponding traffic “rides for free” on the spare backhaul bandwidth made available by Cisco Abis optimization solutions (Figure 1-3).

Figure 1-3 Cisco MWR 2941-DC Router in a Cell Site POP—Example

Note The Cisco MWR 2941-DC router does not currently support UMTS Iub optimization.

RAN-Optimization Implementation

In RAN-Optimization (RAN-O), the Cisco MWR 2941-DC router extends IP connectivity to the cell site and base transceiver station (BTS). The router provides bandwidth-efficient IP transport of GSM and UMTS voice and data bearer traffic, as well as maintenance, control, and signaling traffic, over the leased-line backhaul network between the BTS and leased-line termination and aggregation node through compression (cRTP/cUDP) and packet multiplexing (Multilink PPP).

Cisco IOS Software Features

One version of the software is required for implementing the Cisco MWR 2941-DC router.

Out-of-band master mode not supported—This release does not support out-of-band master mode for Timing over Packet/adaptive clock recovery. If your network design requires out-of-band master clocking, you can use the CEoPs SPA on the 7600 router for this purpose.

Limited OSPF support—Bidirectional Forwarding Detection (BFD) is supported on VLAN interfaces only. OSPF is the supported BFD client. When BFD and OSPF are used together with layer 2 redundancy applications such as Flexlink and a layer 2 network failure occurs, the Cisco MWR 2941-DC attempts to reestablish layer 2 redundancy. If the Cisco MWR 2941-DC cannot reestablish layer 2 redundancy before the defined BFD detection timeout, it attempts to re-establish BFD and OSPF redundancy using an alternate layer 3 path. If BFD detects a layer 3 failure while the Cisco MWR 2941-DC is attempting to reestablish layer 2 redundancy, increase the BFD timeout value.

T1 SAToP is not supported on the HWIC-4T1/E1.

L3VPNs (also known as MPLS VPNs) are not supported.

New Features in Cisco IOS Release 12.4(19)MR2

The following features are supported in release 12.4(19)MR2 of the Cisco IOS software:

The following features are supported in release 12.4(19)MR2 of the Cisco IOS software:

PWE3 Circuit Emulation over PSN (Packet Switched Network)—Allows you to create pseudowires (PWs) that emulate unstructured and structured T1s and E1s over an MPLS infrastructure, down to NxDS0 circuits. The Cisco MWR 2941-DC supports the following PWE3 standards:

Clocking features—Cisco IOS Release 12.4(19)MR2 introduces several new clocking features that are supported on the ASM-M2900-TOP daughter card, also known as the RTM Module. The RTM module supports the following new clocking features:

– Precision Time Protocol (PTP)—Clocking and clock recovery based on the IEEE 1588-2008 standard; allows the Cisco MWR 2941-DC router to receive clocking from another PTP-enabled device or provide clocking to a PTP-enabled device.

– Adapative Clock Recovery (ACR)—Also known as Timing over Packet (TOP), this feature allows the MWR 2941 to use in-band or out-of-band clocking on a virtual or regular TDM pseudowire interface. ACR allows the Cisco MWR 2941-DC to recover clocking from the headers of a packet stream and is compliant with the G.823 and G.824 standards. You can use the recovered-clock slave command to configure out-of-band clock recovery and the recovered-clock recovered adaptive command to configure adaptive clock recovery.

Synchronous Ethernet—Allows the network to transport frequency and time information over Ethernet. You can use the network-clock-select command to configure synchronous Ethernet.

IMA—This feature allows you to connect one or more interfaces to an ATM network using Inverse Multiplexing ATM (IMA). You can define IMA groups that can contain up to 8 bundles, with up to 24 links per bundle.

IP Header Compression over PPP—This feature introduces support for IP header compression over PPP that is compliant with RFCs 2507, 2508, and 3544.